1. Field of the Invention
The present invention relates to an apparatus and method for detecting leads off in a multi-electrode medical diagnostic system, more particularly to an apparatus and method for detecting leads off in a multi-electrode medical diagnostic system employing the theorem of parallel connecting the input impedances of the leads.
2. Description of the Related Art
Because a multi-electrode medical diagnostic system such as a 5-electrode ECG machine was widely used, it will become an important issue how to detect the connecting condition between all the leads and multi-electrode medical diagnostic system. If leads-off occurs, it will cause the multi-electrode medical diagnostic system to receive wrong or incomplete physiological signals from patients.
A lead includes an electrode and a conductor. A leads-off refers to any lead is separated from a patient""s skin and thus a leads-off occurs between the lead and multi-electrode medical diagnostic system. A prior art method for detecting a leads-off between the lead and multi-electrode medical diagnostic system is accomplished by detecting the change in the lead impedance. The impedance includes electrode impedance, conductor impedance and electrode-to-skin connection impedance. When the lead is separated from a patient""s skin, a high electrode-to-skin connection impedance would be created. By means of detecting lead impedance, it will be known if the lead is separate from a patient""s skin. The prior art measurement method is to apply a dc voltage to every lead through respective loading impedances. When the lead is disconnected from a patent""s skin, the output voltage level of an amplifier will be pulled high because the voltage relative to the electrode is separated from the reference, ground. When the output voltage of the amplifier exceeds the threshold value, it means that a leads-off occurs. The above method was disclosed in U.S. Pat No. 4,577,639. However the prior art method in which dc voltage is used will corrupt the patient""s physilogical signals especially, the RL lead as a reference ground is disconnected, it will be mistakenly considered that all the leads are disconnected from the patients skin. Another prior art method of detecting a lead disconnection is to use two sets of high frequency carrier signals to detect lead impedance and thoracic impedance, and separating the lead impedance and thoracic impedance by means of demodulating and filtering. When the signal of lead impedance is over the threshold value, it means a leads-off occurs. The above method was disclosed in U.S. Pat. No. 4,919,145 and U.S. Pat. No. 5,020,541. The disadvantage of the method is that only three lead impedance signals (Leads I, Leads II and Leads V) will be measured, so that the correct location in which leads are disconnected is difficult to find out. For example, if the Leads I was disconnected, it is hard to determine that one lead or two leads were disconnected, it is also hard to determine which one of the RA lead or LA lead is connected if only one lead was disconnected. Besides, there is no way to detect whether the RL lead is disconnected.
As above described, the prior art methods do not have an efficient way to detect the correct disconnection location of sole or multiple leads (as U.S. Pat. No. 5,020,541), or to detect if a RL lead is disconnected (as U.S. Pat. No. 5,020,541 and U.S. Pat. No. 4,577,639).
The object of the present invention is to resolve the prior art disadvantage of no way to detect the correct disconnection location of a sole or multiple leads, or no way to detect if a RL lead is disconnected. To accomplish the object, this present invention proposes an apparatus that can detect the leads-off, multi-lead ECG and impedance pneumography, and provides a solution to detect the correct disconnection location of the multiple leads and to determine if the RL lead is disconnected. The apparatus of the present invention can inform a physician to recover a fine connection between leads and multi-electrode medical diagnostic system so as to obtain a good quality medical measurement. Furthermore the apparatus of the present invention doesn""t have any switch circuit, and thus the complicated circuit control is not needed.
The invention discloses an apparatus for detecting leads-off of multi electrode medical diagnostic system, said apparatus comprising: a carrier circuit unit connected to a plurality of active electrodes and a reference electrode connected to a patient to be detected for generating a plurality of carrier signals of leads and impedance pneumography; a prestage protecting circuit coupled to the carrier circuit unit is to protect the apparatus during defibrillation and generating a plurality of input impedance signals; and a leads-off detection unit coupled to the carrier circuit unit for demodulating the plurality of input impedance signals into lead voltages. This present invention can further comprises a central processing unit and an analog-to-digital converter for receiving the output of the leads-off detection unit, and calculating the amount and the position of lead off situation, depending on an algorithm embedded in the central processing unit.